This invention relates generally to host computer systems and peripherals. More specifically, the peripherals have a Personal Computer (xe2x80x9cPCxe2x80x9d) card form factor, the card being externally and removably coupled to a host system. The invention relates to structures and configurations of such a card, particularly for implementing mass storage peripherals such as electrically erasable programmable read-only-memories (EEPROM) or Flash EEPROM system.
Computer systems typically use high speed semiconductor random access memory (RAM) for storing temporary data. However, RAM is volatile memory; that is, when power to the computer system is disconnected, data stored in RAM is lost.
For long-term, non-volatile storage, two types of memory are typically employed. One type is magnetic disk memory intended for mass storage with practically unlimited number of write operations. The other type is semiconductor memory, traditionally intended for storing a relatively small amount of data (e.g. system parameters) with no or limited number of write operations.
When mass storage is desired, magnetic disk drives, whether fixed or removable, are generally more economical and more amenable to write operations than solid-state memory. Typically, a computer system employs a combination of fixed and removable (floppy) magnetic disks. However, they are relatively slow, bulky and require high precision moving mechanical parts. Consequently, they are not rugged and are prone to reliability problems, as well as being slower and consuming significant amounts of power.
The undesirable features of magnetic disks become even more acute with the advent of portable and mobile computing. Disk drives are obstacles in the quest towards greater portability and lower power consumption of computer systems.
Non-volatile semiconductor or solid-state memories have the advantage of being speedy, light-weight and low-power. Examples are ROM, EEPROM and Flash EEPROM which retain their memory even after power is shut down. However, ROM and PROM cannot be reprogrammed. UVPROM cannot be erased electrically. EEPROM and Flash EEPROM do have the further advantage of being electrically writable (or programmable) and erasable. Traditionally, these semiconductor memories has been employed in small amount for permanent storage of certain computer system codes or system parameters that do not change.
There is currently underway an effort to apply non-volatile Flash EEPROM memory systems for mass storage applications. For example, they are intended to replace either of the existing fixed or removable floppy magnetic disk systems, or both. Such systems are disclosed in commonly assigned and copending U.S. patent applications Serial No. 07/684,034, filed Apr. 11, 1991, COMPUTER MEMORY CARD HAVING A. LARGE NUMBER OF EEPROM INTEGRATED CIRCUIT CHIPS AND MEMORY SYSTEMS WITH SUCH CARDS, now abandoned and Ser. No. 07/736,732 filed Jul. 26, 1991, COMPUTER MEMORY CARDS USING FLASH EEPROM INTEGRATED CIRCUIT CHIPS AND MEMORY-CONTROLLER SYSTEMS, now abandoned. Relevant portions of these disclosures are incorporated herein by reference. It is now becoming possible to fabricate a few megabytes of Flash EEPROM on a single semiconductor integrated circuit chip. As a result, several megabytes to tens of megabytes of memory can readily be packaged in a physically compact memory card, the size of an ordinary credit card.
Indeed, a series of industry xe2x80x9cPC Card Standardsxe2x80x9d are now being promulgated by the Personal Computer Memory Card International Association (PCMCIA), Sunnyvale, Calif., U.S.A. Excerpts of the current PCMCIA Standards, Edition Release 2, dated Nov., 1992 are incorporated herein by reference. These standards set mechanical (Types I, II and III) and technical (Revision 1.0, 2.0) specifications for a memory card and its connection to a host.
The PCMCIA card has the form factor approximately the size of a credit card and is externally connectable to a host computer system via the PCMCIA interface. Originally, these cards were intended as memory card add-ons for portable or mobile computing systems. Soon thereafter their standards were expanded to accommodate other peripherals such as modems, network adapters, and hard disks. Thus, PCMCIA Type I card is 3.3 mm in overall outside thickness, less than 5.5 cm in width, and less than 9.0 cm in length. Types II and III have similar dimensions, except Type II card is 5 mm thick and Type III card is 10.5 mm thick. Revision 1.0 of the technical specification dated Sept. 1990, is a memory-only standard for memory card applications. Revision 2.0, dated Sept. 1991, is a standard with added input/output (I/O) capabilities and software support suitable for other non-memory types of peripherals.
In memory card applications, such PC cards have been commercially implemented primarily using either ROM or SRAM, with SRAM made non-volatile through backup battery. These solid-state memories operate and function under similar conditions as RAM, in that they are directly connected to the host""s bus and addressable by the host""s processor. Thus, similar to RAM, they can be simply added to a host computer system without additional hardware or software.
On the other hand, PC cards using EEPROM and Flash EEPROM have quite different properties and operating requirements that make their incorporation into a host computer system not as straight forward. Typically, additional hardware such as a controller and software are required to control the operations of the EEPROM or Flash EEPROM. The controller generally provides the necessary voltage conditions for the various memory operations. In more sophisticated implementations, it can communicate with a host via a standard disk drive interface, store the data under a prescribed file structure in the Flash memory (e.g. compatible with a standard disk operation system), and handle any errors that may arise.
The requirement for additional support hardware (e.g. controller) and software (e.g. microcode or firmware and drivers) in these devices poses issues of cost and inflexibility in memory configuration as well as system updating and upgrading. For example, when Flash EEPROM PC cards are used to replace magnetic floppies or other removable storage, the additional support hardware to implement the control functions may contribute significantly to the cost and other overhead of the product relative to the memory capacity they provide.
Similar considerations also apply to other types of peripherals, such as hard disks, modems and network adapters. Their support hardware and software tend to add cost, overhead and inflexibility to the final products.
Accordingly, it is a general object of the invention to provide a peripheral in the form of a PC card that can be removably connected to a host system from the external of the host system, and that is cost-effective and flexible in configuration.
It is an object of the invention to provide such a PC card with a specific type of semiconductor memory system having non-volatility, ease of erasing and rewriting, speed of access, and further being compact, light-weight, low power, low cost, reliable, and flexible in configuration.
It is another object of the invention to provide a removable memory card that is removably coupled externally to a host system via a standard interface such as a PCMCIA interface.
It is another object of the invention to provide a comprehensive PC card that is adapted for use in a number of peripheral applications.
It is a particular object of the invention to provide low cost Flash EEPROM memory cards, for example to replace floppy disks, magnetic tapes, or photographic recording films.
It is another object of the invention to provide a removable PC card that can accommodate components off-loaded from the host system in order to minimize the size and cost of the host system and to provide flexibility in system configuration.
It is yet another object of the invention to provide a removable card that can interface either directly to a host system via an interface native to the card or indirectly via a standard interface to the host system.
It is yet another object of the invention to provide a removable card that stores encoded data that can be decoded when the card is relocated from one host system to another.
These and additional objects are accomplished by the various aspects of the present invention, either alone or in combination, the primary aspects being briefly summarized as below.
The externally removable PC card is constituted from a mother card portion and a daughter card portion. The daughter card portion is removably coupled mechanically and electrically to the mother card by means of a mother/daughter interface. The mother card portion can be removably coupled to a host system externally by means of a standard interface that provides both mechanical and electrical connection. In operation, the mother card portion and the daughter card portion are coupled by the mother/daughter interface to form an integral PC card, and the integral PC card is removably coupled to the host system.
Partitioning the externally removable PC card into a mother card and daughter card portion allows the functional components of a peripheral implemented on a PC card to be advantageously partitioned.
According to one aspect of the invention, the peripheral implemented on the PC card is a flash EEPROM system, comprising flash EEPROM chips and supporting hardware circuits that form a controller for controlling the operations of the flash EEPROM and for interfacing to the host system. The flash EEPROM system is partitioned such that the controller resides on the mother card and the flash EEPROM chips reside on the daughter card.
In this way, a more cost-effective memory system is possible, especially in applications where magnetic floppy disks are to be replaced. This is because each daughter card containing only flash EEPROM acts essentially like a semiconductor flash EEPROM xe2x80x9cfloppy diskxe2x80x9d, and need not have a controller on it. The one controller on the mother card can then serve any number of these flash EEPROM xe2x80x9cfloppy disksxe2x80x9d. The cost of each flash EEPROM xe2x80x9cfloppy diskxe2x80x9d is therefore significantly reduced by elimination of the controller on the xe2x80x9cfloppy diskxe2x80x9d itself. The other advantage is an increase in system flexibility. The user can add or decrease memory capacity by choosing among daughter cards with various amount of installed memory chips. Also, with each update or upgrade of the controller, only the mother card need be replaced, the daughter card xe2x80x9cfloppy diskxe2x80x9d being fully usable with the new mother card.
According to another aspect of the invention, a PC card is implemented with a comprehensive mother card portion containing the common functional components of a number of peripherals. Each peripheral then has the rest of the functional components residing on a daughter card. For example, a magnetic hard disk, a modem, and a network adapter all have common functional components similar to that of a flash EEPROM system, such as a host interface, a processor, and a ROM. By moving these common functional components to a comprehensive mother card, each individual peripheral will have less components on the daughter card, thereby reducing cost.
According to another aspect of the invention, some of the hardware originally residing in the host system is relocated to the mother card. One example of such a hardware is system memory (DRAM, SRAM, or flash) or even the host microprocessor. The relocation is advantageous because most small palmtop/notebook computers will not have sufficient room (i.e. Motherboard space) to include a lot of system memory. Furthermore, these units are too small for users to open up and upgrade with memory SIMM modules. Also, most manufacturers prefer to ship out the lowest cost base unit with minimum memory. This can be accomplished by using the Mother/daughter PC card, with the mother card carrying the controller and main memory (capacities can be e.g. 0.5 MB, 1 MB, 2 MB, 4 MB, 8 MB, etc.), and the daughter card carrying either flash memory xe2x80x9cfloppy drivexe2x80x9d or a small form factor magnetic hard disk (e.g. just the head, disk and motor assembly portions of a 1.8xe2x80x3 or 1.3xe2x80x3 hard disk without its controller logic), or a microfloppy, or even a miniature tape backup drive. Essentially, the Mother/daughter PC card contains all the memory requirements of the host system, i.e. the palmtop/notebook computer, which will free up precious space on the computer motherboard.
According to another aspect of the invention, the mother card is adapted to removably receive a plurality of daughter cards. In this case, more than one mother/daughter connector may be provided on the mother card for removably receiving a plurality of daughter cards. The same controller on the mother card controls and services any number of daughter cards that are coupled to it. In one embodiment where the daughter cards are flash EEPROM, they are all controlled by the same controller on the mother card. This is similar to having a multiple floppy drive capability. In another embodiment where the daughter cards are a mixture of peripherals, such as flash memory and a modem or other communication peripherals such as LAN adapter, or wireless fax modem. The same controller acts as a coprocessor or a sub-host system services the mixture of peripherals coupled to it. For example, the controller can receive fax data through a fax modem daughter card and store it in a flash memory daughter card.
According to another aspect of the invention, the removable daughter card has the option of working with a host system in conjunction with a mother card externally coupled to the host system. The mother card serves to furnish support components, such as a comprehensive controller and optional functional components, necessary for the operation of the peripheral device implemented on the daughter card. At the same time, it adapts the native interface of the daughter card to the standard interface of the host system. At the same time, the daughter card has the option of working directly with a host system via the native interface of the daughter card if the support components are built into the host system.
In this manner, a comprehensive, removable daughter card functions with a host system either directly when the host system is customized with the support components or indirectly via a mother card having the support components thereon, the mother card being connectable to the host system via a standard interface. This provides flexibility and system compatibility on the one hand and economy and convenience on the other.
According to another aspect of the invention, when the support components includes data encoding and decoding processing functions such as compression and decompression, encryption and decryption, the key or algorithm for recovering the data is stored with the daughter card. In this way, irrespectively of how the data is encoded by one host system, when the daughter card is relocated to another host, the information for decoding it is always available.
According to another aspect of the invention, the removable daughter card has identifying data that is readable by the mother card or the host system coupled thereto. The identifying data includes information that identifies what type of peripheral device is implemented on the daughter card. In another embodiment, the identifying data includes an identity code assignable to the daughter card for operational expediency and security applications. The device type identification allows the support components such as a comprehensive controller as well as the host system to configure and adapt accordingly. It further provides a form of acknowledge signal in a connection protocol for the native interface of the daughter card. The unique identity code provides a basis for matching each removable daughter card to a specific host system or mother card, for managerial or security reasons.
Additional objects, features and advantages of the present invention will be understood from the following description of the preferred embodiments, which description should be taken in conjunction with the accompanying drawings.